The present invention is in the field of mechanical linkages, and more particularly, relates to linkages for controlling motion of an element to be along a reference axis.
Linkages for constraining motion of an element to be along a reference axis are particularly useful in weighing systems, or scales, where it is desired to sense the weight of an object. Such systems require transfer of the gravitational force of the object, for example, in a weighing pan, to a force sensor without the introduction of error components due to friction and other sources. Typically, off-center loading of the object in the pan leads to moments being applied to the various elements linking the pan to the sensor. These moments, in turn, generally produce additional forces along the sensitive axes which may cause measurement error.
In the prior art, it is known to reduce the effect of off-center loading by coupling the weighing pan to the sensor by a parallelogram linkage. In one form, a pair of V-shaped flexure (or hinged) elements, each having a vertex portion and a pair of distal end portions, is configured with the distal end portions being affixed to a support member or casing, so that the V-shaped members lie in parallel planes. A connecting link is fastened between the vertex portions of the flexure elements. With this configuration, in order to precisely constrain the motion of the reference member coupled to the link to a motion along that reference axis, the V-shaped elements must be precisely positioned with respect to the support member in order to achieve the desired parallelism. With this configuration, the motion of the reference member is highly resistant to applied moment. However, as a practical matter, the precise positioning of the V-shaped elements requires critical alignment of those elements during fastening the distal ends of those elements to the support member.
It is an object of the present invention to provide an improved linkage for constraining the motion of an element to motion along a reference axis.